Electrical risers ensure supply-relevant feeding of electrical power over electrical lines in or on buildings. Typically, the respective primary connections are led vertically into the various floors of the building, starting from the main building power supply, and are then branched into secondary connections. Thus, electrical risers make an essential contribution to functional integrity in building services technology, and to the necessary safety-relevant systems.
Due to this special importance, basic requirements for functional integrity apply to electrical risers. They must be designed in such a way that the safety-related installations and devices that rely on a power supply remain functional for a sufficient period of time, even in the event of fire. These safety-related installations and devices just mentioned include, for example, safety lighting, fire mode control of passenger elevators, fire alarms, and systems for alerting and provision of instructions.
An electrical line system is made up of one or more electrical cables and a support structure. The electrical cables must be supported by the support structure in accordance with DIN VDE 0100-520 and DIN 4102-12. If the support structure provides for a layout of an electrical cable in the vertical direction, it is referred to as an electrical riser. A plurality of risers may be vertically guided in parallel in a so-called riser conduit through a building.
In particular in large buildings, a plurality of electrical risers designed as parallel power cables or data cables are required. In this case, instead of customary round cables, flat cables are used, which can guide the approximately 90 line cores in parallel to one another.
For a continuous tensile stress on cables and line systems due to the intrinsic weight, for example, DIN VDE 0100-520, Section 522.8.1.4 requires that for a vertical layout, the type of line design, the cross section, and the type of fastening must be suitable, as required by Section 522.8.1.3, to effectively avoid damage due to the intrinsic weight. For this reason, in riser conduits, risers are generally separately fixed to suitable walls with cable clamps at predefined intervals. The interval spacing depends on the weight of the cable per meter.
Support structures for riser conduits that are not directly fastened to the wall are generally made up of a vertical ladder in which rungs or profile rails are horizontally attached, with a maximum spacing of 300 mm, to two vertical retaining rails. The cables in the riser conduit are supported on each rung or profile rail via suitable single clamps or bracket clamps.
Unlike the situation for a horizontal layout, in which electrical lines on their support structures may be combined into groups of many cables in cable ducts, vertically guided electrical cables must be either fixed separately by single clamps, or, in the case of round cables, put together with bracket clamps, using up to three cables, although the spacings of the electrical cables in the bracket clamp must correspond to the spacing for a layout of single clamps.
In the context of fastening electrical lines, but in particular for installing electrical risers, cable clamps in the form of single clamps or bracket clamps having a corresponding clamping effect are generally used. Cable clamps are known for round cables as well as for flat cables. A cable clamp functions according to the clamping principle. It surrounds the cable in such a way that the insulation of the cable is firmly enclosed. The size of the cable clamp to be used is a function of the cable diameter in order to ensure the required support. The relief of load from the weight results from fastening the clamp to the support structure or to the wall. For a bracket clamp, multiple such single clamps are combined into a unit that is fastened to the support structure or wall. A bracket clamp may hold up three cables in this way, with the radius of an individual cable, in the case of round cables, being 25 mm maximum. Instead of a clamp that completely surrounds the cable, clamps are also known that have an opening on one side. These clamps are placed on the cable and fixed to the wall, generally using screws, so that the cable is clamped between the wall and the clamp.
In addition, clamping devices for various clamping items are known from DE 102006021555 (A1), EP 0296537 (A2), U.S. Pat. No. 4,318,563 (A), or DE 10240551(A1), for example.
To meet fire protection regulations, the test requirements for electrical line systems according to DIN 4102-12 with functional integrity classes E30, E60, and E90 apply. Thus, for example, in safety-related systems a fire resistance period of 90 minutes (E90) for the electrical line system must be ensured. The actual fire resistance period of a line system is determined by the characteristics of the cable and also by the support structure of the electrical line system.
Depending on the characteristics and layout of a cable as well as the design of the power supply, a distinction is made between basically two forms of support structures for fire functional integrity. A standard-specific support structure implements the parameters defined in DIN 4102-12, based on specified criteria. A cable-specific support structure is a tested cable system based on DIN 4102-12, with defined deviations.
A special requirement applies for risers under DIN 4102-12 8.3: active support of the cable with functional integrity must be provided in the event of fire. The aim is to ensure that the electrical line system, as an overall structure, consistently meets the requirements of its functional integrity class. Risers are particularly at risk here. Although cables in the riser must already be supported at suitable intervals and relieved of load on account of their high weight to prevent the line from tearing away, in the event of fire the support required under DIN VDE 0100-520 is no longer adequately provided by single clamps and bracket clamps. The diameter of the cable decreases due to melting of the cable insulation in the event of fire. The cable clamps that are adapted to the cable diameter during installation then can no longer prevent slipping through, and the intrinsic weight of the cable is thus no longer supported. To achieve an effective support mount under DIN 4102-12 8.3, the following approaches to the stated standard are generally known:    1. In addition to the general support by cable clamps at predefined intervals, the cable is also supported by a lateral, horizontally extending projection of at least 300 mm after every 3500-mm vertical interval of the riser conduit (meandering layout). The support by a meandering layout requires appropriate space in the surroundings of the riser. This is taken into account from the outset in the planning of the riser conduit.    2. In addition to the general support by cable clamps at predefined intervals under DIN VDE 0100-520, installation of a strain relief device in riser conduits is known. This strain relief device is made up of a fire-resistant attachment, generally made of mineral fiber boards, that is mounted on the riser conduit at predefined intervals of 3500 mm. Since only the weight of a 3500-mm length of cable is suspended on this strain relief device due to the interval control, the aim is to reduce the risk of the cable tearing off, even in the event of fire. The strain relief device is based on the principle of thermal insulation. By protecting the fastening points, to which the risers are fixed with cable clamps, by a heat-resistant cover, the objective is to delay melting or burnoff of the line insulation at the fastening points.